I'm sure it's been covered but hearing it more than 1ce makes it believable...Car type makes no difference...I know a guy with a mighty boy running 2 15plate 750CCA deep cycle batts 4 a stereo. The back tray is an eski. Just add booze n u have the ultimate party machine. U r best replacing yor battery with a deep cycle for the purpose of the trip and keep in mind a 3way fridge may not freeze but will use less pwr than a motorised item. Also, u could place it in a $30 battery box in your luggage compartment and wire it up with or w/out an isolator solenoid but I would use 1 to save bein stuck with 2 flat batteries. I can supply u with a simple wiring diagram if u like to complete this and I can show u how to make it so u can remove the 2nd batt w/out hassles at any time.

The CCA (Cold Crank Amps) of the battery means f_ck all realistically when talking about deep cycle batteries.

You want the to know the RC in AH as previously mentioned.

I have 650CCA Optima yellow top spiral cell batteries. But they are only 55AH of RC on the other hand I have about fourteen 110AH of RC deep cycle batteries, they dont even list a CCA ratting. Which one is better for starting - undoubtedly the optima. Which is better for Deep cycle applications - undoubtedly the 110AH battery.

Car type makes little or no difference. How ever the capability of the alternator does. You want the alternator to be able to charge the batteries including replacing the joules taken out by starting (starting = friction = torque req'd = current = heat = more current due to voltage drop caused by heat = more heat = more resistance etc etc.)

It also dictates which sort of isolator would be best used and also gives us an idea of under bonnet space available

A place I'd rather be...Mitchel Road, Bomjinna. Central West Victoria (Jan '08)

I ended up going to TJM. They suggested getting something similar to what Cruzin suggested - an AGM battery in a battery box - branded as a Waeco. This was without checking if it was possible to fit an auxilary battery in the car.

One thing he did mention was that if the fridge was connected to the battery pack while the battery pack was being charged by the running car, it is unlikely it would be able to charge faster than the fridge consumed the power. Does that sound right?

Car type makes little or no difference. How ever the capability of the alternator does. You want the alternator to be able to charge the batteries including replacing the joules taken out by starting (starting = friction = torque req'd = current = heat = more current due to voltage drop caused by heat = more heat = more resistance etc etc.)

It also dictates which sort of isolator would be best used and also gives us an idea of under bonnet space available

Mostly true but a deep cycle batt also likes a trickle charge so an 80-100A alt should be plenty (depending on batt) but it will charge better on long trips. Isolator makes little diff as long as it gets charge when motor is running and isolates when ign is off, leaving normal batt 4 starting etc. A deep cycle may not b ness but at least a lge batt, n if u know what cca does in a batt it does speak 4 a lot...basicalyy means how long u can turn yor motor over in the morning b4 it dies...similar to amp hrs, which mostly applies to working out how many amps u will b drawing as to how long the batt will last. Knowlege of bonnet space is useless unless it is a big 4x4 with dual batt capabilities. Engine space is ltd on anything after 1985.

CCA rating of a battery only gives an indication at full discharge. not all motors require the torque and most motors that do use gear reduction starters now days.Also CAA does take into acount a batteries "natural recovery" (which actually doesnt exist its just a shifting of energy) and a larger RC will have a greater recovery. Also CCA allows the batteries to go to a much lower voltage for a short period (often a vehicle starting will drop the voltage in a battery to or even below 7V) because they assume they will be quickly charged by the alternator.

Most WET deep cells only take a slow charge. many of the AGMs will take a full 80amp charge! that a hell of a lot of current draw and looking under the bonnet of most cars it like to see that piss ant 8ga (8mm^2) charging cable pump out 120amps like the alternators are generally rated at on modern vehicles for must more than a couple of seconds and even then it would be a a reduced voltage due to the nature of electromagnetic alternators.

At the end of the day if you have a second battery you are more than likely going to drive for a couple of house and even at a moderate charge rate thats probably close to 100amps pumped into the batteris over that period

This is meant 2 b met with a smile & friendly tone; Gees mate...either u r an electronics tech or u got a lot of time on yor hands and a serious interest in elctricals hehehe. Unfortunately I am only a mech not an auto sparky so my knowledge is limited & I don't know enuf 2 dissagree (makes sense tho) ...but...it sounds like u know wot the best batt 2 suit his car n his needs would b by far. If u set him up with the right batt, put in a box with an isolator then an in line anderson plug (mounted in a safe place)...I think it would b a case of prob solved.

Started playing around with 240V AC when I was about 7 (that was a little bit silly!) Then I got into Pro Audio @ 13 and continued playing with pro Audio and a little bit of Pro lighting. (got out of the pro Audio thing at about 19 when an X-Array bin got dropped on me bumping out a 64 bin rig)

Then I got heavily involved with Car Audio. And inparticularly Car Audio Competition - I judge SQ (Sound Quality) which includes a safety component regarding batteries and cables etc. I also compete in SPL (Sound Pressure Level - or Subwoofer comps) competition where its not uncommon for us to draw in excess of 800 amps so I've learned a LOT about batteries how they work different battery and energy storage devices and how best to get power from a to b with minimal voltage loss Best score so far for me is in full street trim 144.3dB @ 58htz (for those of you who know about sound wave formation and / or physics you would understand that a LOT of energy being displaced - and thats louder than standing 50 meters from a jumbo at take off and approximately 8 times as loud as a rock concert :D

Im also the state rep for Mobile Electronics Australia. I've got a lot of freinds in the industry including some of the best show car builders in Oz. (in fact if any of you know the Alpine Electronics 300C the builders of that car are very good freinds of mine - same guys built the Eclipse Tarago)

So bearded shark sorry if ive come across abruptly (I know I can at times) Its just (unfortunately?) part of my personality

But its all good from my end so as long as i havent offended you I'm all happy!

A place I'd rather be...Mitchel Road, Bomjinna. Central West Victoria (Jan '08)

Well, I finally went out and laid down some cash for a fridge and battery. Decided not to go for a dual battery setup partly due to cost. I ended up getting a second hand 65A/H AGM battery previously used in a UPS system for $88 and will buy a good 240V charger to maintain the battery well. Should last me 2-3 days which should be plenty as our stays at unpowered sites are few and far between. Decided not to get an 80-120A/H battery because storage space in the back of the car was already at a premium.